I went back to the shop (cashed in a gift certificate on a new card reader - nice), and attached my strap. It felt okay with that. I still have to slip out of the strap for an underhand portrait hold, but I guess I could live with that.

The interesting thing was, when I took the strap off again the grip felt much better than the first time I handled it. I had to take a deliberate grasp with my hand rotated back a little, rather than just grabbing it like I can with the 450D.